GEO101L Earth Science
Module 3 Lab: Soil Porosity and Permeability
Soils are made up of particles of rock, along with the spaces between those particles. Physical characteristics of soil particles, such as size and shape, can influence how water moves through them. Aquifers are underground layers of rock that are capable of storing water. An aquifer is recharged when water filters through the soil levels above it.
In this lab you will investigate the characteristics of known and unknown soil samples. The Lab Kit includes gravel, sand, and top soil samples, and you are to get a local sample from the soil at your home or a potted plant in your house.
This lab will look at the porosity and permeability of these soil samples. Porosity is the basic measure of how much of its volume is open space. We will express porosity as the percentage of pore space in a material’s total volume.
This lab will also look at permeability of these soil samples. Permeability is a measurement of how easily liquids flow through soil samples. We will calculate each sample’s drainage rate as well as percentage of water retention.
Experiment 1:
Methods to Measure Soil Porosity 1. Pour 100 mL of water into your 250ml plastic beaker and draw a line to indicate the water level in the beaker. Write 100 mL in the total volume column on your data sheet. Save this water since you can use it again.

2. Fill the 250ml plastic beaker with the first soil sample up to the line you drew (100ml).

3. Using your graduated cylinder, slowly and carefully pour water into the beaker until the water reaches the top of your sample. Write the volume of water remaining in the graduated cylinder on your data sheet.

4. Subtract the volume remaining from the total volume. This is the amount of water you added to your sample. Write the volume of water added to the sample on your data sheet – this is the pore space.

5. To determine the porosity of the sample, divide the pore space volume by the total volume and multiply the result by 100. Write the porosity on your data sheet. (Note: % pore space = pore space / total volume x 100)

Description of Sample | Total Volume(ml) | Volume Remaining in the Graduated Cylinder(ml) | Pore Space | Porosity (% pore space) | Gravel | | | | | Sand | | | | | Top Soil | | | | | Your collected sample | | | | | | | | | |

Questions 1. In your own words. define porosity.

2. If you were an environmental engineer, where would you recommend placing a drinking water well after learning about soil porosity and permeability? Explain why.

3. Which soil sample that you tested had the greatest risk of transferring harmful chemicals into a drinking water aquifer? Explain why.

Experiment 2: Soil Permeability
Methods to Measure Soil Permeability
Please read through the directions before starting your experiment.
1. Set up apparatus so the plastic funnel is in the graduated cylinder.
2. Place a piece of filter paper in the funnel so that solid material does not flow through. Watch this short movie on how to fold filter paper http://www.youtube.com/watch?v=or6ex5toLVg
3. Using a beaker, measure 25 mL of your first soil type and place it in the funnel, on top of the filter paper.
4. Using a graduated cylinder, measure 50 mL of water and slowly pour it into the funnel. Let the water percolate through the soil and collect it in the graduated cylinder below. BEGIN TIMING AS SOON AS THE WATER TOUCHES THE SOIL SAMPLE.
6. Continue to time until the water has stopped collecting in the beaker. Record the total amount of time for each sample in the corresponding drainage time data area in the table.
7. Measure the amount of water in the graduated cylinder and record this number in the data table under the amount of runoff (measure in mL).
8. Clean all equipment. Save soil sample since you may need it again.
9. Repeat steps #1-8 for the rest of the soil samples. Record all data in the table.

Description of Sample | Drainage Time(sec) | Amount of Runoff(ml) | Drainage Rate(Amount of water drained/time) | % Water Retained((50ml –amount of runoff)/50)*100 | Gravel | | | | | Sand | | | | | Top Soil | | | | | Your Collected Sample | | | | |

Questions 1. In your own words define permeability.

2. The sample that had the highest drainage rate and retained the least amount of water was the most permeable. Which soil sample fit that data? Explain why.

3. Why can some soil samples hold more water than others?

4. Why are pore spaces in soil important to plants and organisms that live there? 5. Looking at the data for soil porosity and permeability, is there a connection or relationship between a soil’s permeability and porosity? 6. Which of these soil samples would you want to place in an area that is known to get sudden downpours of precipitation? 7. Suppose a plant grows in soil with poor water-retaining capacity. What kind of root system do you think would be most beneficial - a deep tap root or a shallow wide-spreading root system? Explain why. 8. Which of these soil samples do you think would be best to build a landfill on? Explain why.